TiO2 is widely used as a non-toxic, stable and inexpensive photocatalyst. TiO2 has a band gap of 3.2 eV, and the light absorption range of TiO2 is only in the ultraviolet region. A conductivity of photoelectron-hole of TiO2 is low, and a recombination rate of the photoelectron-hole of TiO2 is high. Therefore, the photocatalytic efficiency of TiO2 is severely restricted. In the past ten years, composite photocatalysts with heterojunctions have been formed by a combination of photocatalysts having bank structures which are different from TiO2 and TiO2 to improve the photocatalytic efficiency. Because Fermi levels of the photocatalysts with band structures different from TiO2 and TiO2 are different, a directional movement of the photoelectron-hole occurs at the heterojunctions, which causes the Fermi levels of the photocatalysts with band structures different from TiO2 and TiO2 to gradually become uniform and form an internal electric field at the interface. In the photocatalytic process, a rapid separation of the photoelectron-hole can be promoted under the action of different Fermi levels and the internal electric filed, thereby reducing the recombination rate of the photoelectron-hole and improving the photocatalytic efficiency.
BixMoyOz can be used as a visible light catalyst. Valence band of the visible light catalyst is formed by a hybridization of the d-orbital of metal element and 2p-orbital of oxygen element, and a relative valence band is mainly a binary oxide composed of the 2p-orbital of oxygen element. BixMoyOz has a higher valence band positon, the generated hole has a higher potential energy and has a stronger reducing ability, which is beneficial in improving the photocatalytic ability and efficiency. In ACS Catal.6 (2016), 3180-3192, it is stated that increasing the defect concentration of BixMoyOz can improve the photocatalytic activity of BixMoyOz. For example, under visible light irradiation, the photocatalytic activity of a catalyst with TiO2—Bi2MoO6/Bi3.64Mo0.36O6.55 heterojunctions is higher than the photocatalytic activity of a catalyst with TiO2/Bi2MoO6 heterojunctions.